Natural resources such as gas, oil, minerals, and water residing in a subterranean formation can be recovered by drilling wells into the formation. The fluids in the subterranean formation are driven into the wells by, for example, pressure gradients that exist between the formation and the wells, the force of gravity, displacement of the fluids using pumps or the force of another fluid injected into the wells. The production of such fluids is commonly increased by hydraulically fracturing the subterranean formations. That is, a viscous fracturing fluid is pumped into a well to a subterranean formation at a rate and a pressure sufficient to form fractures that extend into the formation, providing additional pathways through which the fluids can flow to the wells.
Particulate matter known as a proppant, e.g., graded sand, bauxite, or resin coated sand, is dispersed throughout the fracturing fluid. The proppant is suspended in the fracturing fluid such that it is deposited into the fractures created by the pressure exerted on the fracturing fluid. The presence of the proppant in the fractures holds the fractures open after the pressure exerted on the fracturing fluid has been released. Otherwise, the fractures would close, rendering the fracturing operation useless. Ideally, the proppant has sufficient compressive strength to resist crushing.
The fracturing fluid is usually a water-based fluid containing a gelling additive to increase the viscosity of the fluid. The gelling additive thus reduces leakage of liquid from the fractures into the subterranean formation and improves proppant suspension capability. The gelling additive is commonly a polymeric material that absorbs water and forms a gel as it undergoes hydration. A foaming surfactant is added to the fracturing fluid. A gas is mixed with the fracturing fluid to produce a foamed fracturing fluid, thus ensuring that the pressure exerted by the fracturing fluid on the subterranean formation exceeds the fracture gradient (psi/ft.) to create the fracture. The surfactant facilitates the foaming and stabilization of the foam produced when the gas is mixed with the fracturing fluid.
After a fracturing fluid has been used to form fractures in a subterranean formation, it is usually returned to the surface. It would be desirable to have the ability to recycle the fracturing fluid to form additional fractures in the same subterranean formation or to form fractures in one or more different subterranean formations. However, conventional fracturing fluids are not suitable for recycling. A need therefore exists for a fracturing fluid that can be recycled several times to fracture one or more subterranean formations.